Means providing separation of exterior sheath of liquid on dispensing tip

Abstract

There is disclosed apparatus in which an aspirating and dispensing tip is provided with liquid wherein residual liquid is left as a sheath on the exterior of the tip after aspiration. The apparatus is improved to include means exterior of the dispensing tip for separating the sheath into at least two parts without detaching residual liquid physically from the exterior surface, the two parts being separated along the axis of the tip by a dry annular portion of the exterior surface having a suitable width. Such separating means is spaced away from the tip a distance effective to prevent contact of the separating means with either the tip or the liquid of the sheath.

What is claimed is: 
     
       1. In apparatus for aspirating liquid into a dispensing container having a dispensing tip and aperture, and means for moving said container and dispensing tip first into the liquid to permit aspiration, and then away from the liquid to permit dispensing of a prescribed volume, said dispensing tip comprising an end surface through which said dispensing aperture extends, said end surface terminating at an edge, said extending tip further including an exterior surface extending from said end surface edge, said exterior surface being subjected to residual liquid which can form a sheath thereon when said tip is immersed in the liquid during aspiration and then removed from the liquid; the improvement wherein said apparatus further includes means separate from said tip for separating said sheath into at least two parts, without detaching residual liquid physically from said exterior surface, said two parts being separated along the axis of said tip by a dry annular portion of said exterior surface having a width effective to keep dispensed liquid from joining both parts, said separating means being disposed so that the separated liquid part closest to said platform edge contacts a surface area on said tip that holds only a volume that is negligible compared to said prescribed volume,   said separating means being spaced from said tip a distance effective to prevent contact with either said dispensing tip or said sheath of liquid.   
     
     
       2. Apparatus as defined in claim 1, wherein said separating means includes an air jet delivering air at a flow rate sufficient to separate said sheath into two parts without physically detaching said liquid. 
     
     
       3. In apparatus for aspirating liquid into a dispensing container having a dispensing tip and aperture, and means for moving said container and dispensing tip first into the liquid to permit aspiration, and then away from the liquid to permit dispensing, said dispensing tip comprising an end surface through which said dispensing aperture extends, said end surface terminating at an edge, said dispensing tip further including an exterior surface extending from said end surface edge, said exterior surface being subjected to residual liquid left as a sheath thereon when said tip is immersed in the liquid during aspiration and then removed from the liquid; the improvement wherein said apparatus further includes at least one air jet spaced from and aimed at said tip, and means for delivering air to said jet at a flow rate sufficient to divide said sheath into two parts separated along the axis of said tip a distance of at least 0.1 cm, without physically detaching said liquid, the part of the liquid which is located adjacent said aperture extending away from said aperture a distance no greater than 900 μm.   
     
     
       4. Apparatus as defined in claim 2 or 3, and further including means for holding said tip within said air flow for at least 0.2 seconds. 
     
     
       5. Apparatus as defined in claim 2 or 3, wherein said distance of said jet from tip is from about 0.05 cm to about 0.4 cm.